$ cp -L /usr/share/dict/words /tmp/test.txt
$ wc -l /tmp/test.txt
99132 /tmp/test.txt
$ du -sh /tmp/test.txt
920K	/tmp/test.txt

$ time perl -MTie::File -e 'open F, "/tmp/test.txt" or die;
  print `ps -orss $$`; my @x = <F>; print `ps -orss $$`'
  RSS
 7408
  RSS
23604

real    0m0.042s
user    0m0.024s
sys     0m0.012s
$ time perl -MTie::File -e 'tie my @a, "Tie::File", "/tmp/test.txt";
  print `ps -orss $$`; $a=$_ for @a; print `ps -orss $$`'
  RSS
 7612
  RSS
55024

real    0m1.001s
user    0m0.908s
sys     0m0.088s